1. Field of the Invention
The present invention relates generally to processing of waste materials, and more particularly to systems and processes for handling organic waste materials.
2. Description of the Prior Art
Landfilling has traditionally been the method of waste handling, but landfilling can cause environmentally unacceptable pollution discharges to the water and, as real estate values increase, is considered to be an unattractive use of land. Thus, current waste management strategies seek to limit the amount of refuse directed to landfills. Recycling and composting programs have become widely accepted for both commercial and residential waste to reduce the demands on landfills.
Generally, recycling programs require separating the waste by type, either at a point of collection (source separated) or further along, such as at a transfer station. Recyclable components can include glass, metals, and plastics, while compostable components can include agricultural wastes, plant matter, food stuffs, wood, cardboard, and paper. Once separated, waste materials are commonly referred to as “source separated,” and source separated materials that are collected together from separate collection points constitute a “single stream.”
Compost facilities have been built to process non-recyclable waste, either in the form of municipal solid waste with provisions for contamination removal, or source separated organic waste. An alternative to composting for non-recyclable waste streams are refuse-to-energy plants where material is burned to create energy. Refuse-to-energy plants first process waste by grinding and then burning the ground material. Although efforts are made to separate out hazardous materials from the waste stream, these plants have had a history of emissions and operational problems related to contaminants. The residual ash created from this burning has also, in some cases, been found to be hazardous.
Anaerobic digestion presents another alternative for handling organic waste materials. The primary objective of anaerobic digestion is the production of a mixture of hydrocarbon gases (“biogas”), which may be utilized as an energy source to generate electricity and/or heat. Any solid material remaining at the completion of the anaerobic digestion process is typically disposed of by conventional landfilling or composted into a soil amendment.
Because of the high capital costs associated with anaerobic digestion equipment, and the environmental issues associated with refuse-to-energy plants, composting has become the dominant method in the United States for the management and re-use of organic waste materials generated in rural and suburban settings. The growing use of composting as a preferred alternative to disposal of organic waste material has also created some environmental problems. These problems include emissions of noxious gases and ozone pre-cursors, runoff from the compost facility, and high energy consumption during material processing. These problems may become particularly acute if the organic waste material contains large amounts of food waste or other high moisture content waste.
Commercial-scale composting is also subject to a variety of financial considerations including capital investment related to accommodating peak seasonal feedstock deliveries, compost process time, and controlling the timing of compost production to match the seasonal demand of the agricultural industry and other compost buyers. Further, the compost produced by these facilities is a low-value product, therefore municipalities have to pay to have the waste accepted.